The use of molds in modern manufacturing of devices is a well known process dating back to ancient times. Most recently, however, precision mold castings have been used by optical equipment manufacturers in the production of optical lenses. Devices incorporating one or more of optical imaging, optical telecommunications, and optical data storage technologies are becoming increasingly prevalent. Many of these products use one or more optical lenses. Consequently, it is highly desirable that the optical lenses used in various devices meet their design specifications as precisely as possible. It may also be desirable to maintain economically feasible manufacturing methods in the production of such lenses so that the lenses may be desirably priced in the marketplace.
As demand for high performance optical equipment has grown, devices have become smaller and more precise. As a result, these devices require difficult-to-manufacture high-precision optical lenses in order to meet performance requirements. The Blu-Ray optical storage standard, for example, uses a short wavelength laser (blue laser) to allow more data to be stored on optical storage discs, as opposed to current standards (CD, DVD) that use red laser light. The shorter wavelength laser requires a smaller, more precise lens with desirably minimal imperfections on the surface thereof.
A current method of manufacturing high-precision lenses is illustrated in FIGS. 1A and 1B, and includes forming a mold cavity 2 into a hard mold material 1, where the mold cavity 2 matches the lens design of a desired optical lens geometry. The mold cavity 2 is generally ground and/or cut from the mold material 1 using at least one of a diamond grinding wheel 10 (show in FIG. 1A and 1B) attached to a movement arm 14 or a diamond turning point 12 (shown in FIG. 2) that perform a predetermined carving algorithm 16 (exemplary, as shown in FIGS. 1A, 1B, and 2). After the final mold Is finished, optical lens material is set inside of the mold and desirably pressed under high temperature and pressure in order to form the optical lens (not shown in FIG. 1). Those skilled In the art will recognize that other methods may be used with the final finished mold to form an optical lens.
It is generally possible to achieve a design precision of around ±0.1 microns using the prior art method described above. However, the grinding/cutting process introduces mold cavity surface errors that do not meet nanometer and sub-nanometer precision required by high-precision optical lenses, such as those needed for the Blu-ray standard. As illustrated in FIGS. 1A and 1B, the surface errors are as a result of undesirable bending of the shank 14 of the movement arm and vibration of the shank 14 and/or the grinding wheel 10. As shown in FIG. 2, similar defects may be caused by bending or vibration of the shaft 20 and/or diamond turning point 12. Undesirable defects may also result from temperature- or pressure-induced changes at the turning point-cavity surface interface 24, as well as the inherent imprecision of mechanical manufacturing tools (not shown in FIG. 2). Furthermore, the grinding wheel/turning point experiences wear and may become less accurate after prolonged use, introducing undesirable manufacturing costs in their replacement and in extra machining of the mold.
Additionally, an optical lens mold 31 having a cavity 32 may be desirably finished with the application of a thin film 33 over at least the cavity 32 (as shown in FIG. 3). The application of the thin film may, for example, prevent undesirable bonding between optical lens material and mold 31 during the pressing process. The application of the thin film, however, may also introduce undesirable undulations on the thin film surface, thereby introducing additional errors to the manufacturing process of high-precision lenses.
Current methods aimed at reducing errors in optical lens manufacturing generally involve the production of an optical lens mold, as described above, from which an imperfect optical lens is produced. Then, an optician manually refines the lens surface to remove surface errors identified from measurements made, for example, with a laser interferometer. Other, more complex, automated methods exist such as magnetorhelogical finishing developed by the Center for Optics Manufacturing (COM) in Rochester, N.Y. However, these processes may introduce additional undesirable surface errors on a lens, and generally do not achieve the nanometer and sub-nanometer precision desirable in higher performance optical devices.